The month that takes its name from the Roman Emperor Augustus Caesar provides us with a prime opportunity to locate a celestial king. This and the small but sure monthly progression back to astronomical twilight (total nocturnal darkness) as the year marches on guarantee that the different items in August’s cosmic performance need not go amiss.
So to commence August’s trip to the constellations if we face in the direction of north and lift our eyes to the highest point in the sky above our heads we can find a special star pattern currently at the zenith. Although visually it’s quite a simple pattern to pick out from the starfield, it’s not a bad one to memorise as it’s also one of the rarer constellations which can be seen all year round, never dropping below Earth’s celestial season-changing horizon. The name of this elite group of constellations with which it shares this status, are the circumpolar constellations. Found within a small concentric ring of patterns endlessly rotating around the pole star, Cepheus the king can be drawn dot-to-dot style with your finger in the heavens rather like an upside-down child’s schema of a house, minus the chimney. As such this stick-figure shape uses up only the five brightest stars in the constellation’s patch of sky. Cepheus, king of Joppa (a city in Phoenicia, now known as Jaffa) was the domineered partner of the royal household, ordered about by his wife Queen Cassiopeia.
Anyone looking for some free celestial entertainment should put 11-13August in their diary and look to the northeast as this is when one of the best meteor showers of the year takes place. Burning through Earth’s atmosphere from the direction of the constellation of Perseus, the Perseids showercould serve up as many as 100 shooting stars in an hour, (about one every minute or so). Although typically quite bright, they are still best spotted after midnight. However we may be assured that with a crescent Moon due to present only a minor luminal distraction at the time, and provided there is no cloud, the Perseids should have a level playing field for showing off their splendour in the heavens.
Having already travelled the equivalent of at least 5000 Earth-Sun journeys (465 billion miles) from the ‘comet cold storage zone’ or Oort cloud around the edges of the Solar System, the lump of ice and dust predicted to be “the comet of the century”, Comet ISON, is maintaining an unexpectedly low profile as it cruises towards our Sun. Although it has recently developed a small tail of dust and vaporised ice, C/2012 S1 ISON’s dim fuzzy form is only currently visible through the largest of telescopes. Our potentially spectacular visitor is now making its way from the constellation of Gemini down towards Cancer the crab, where its downward trajectory has most recently seen it sweep beneath Gemini’s brightest star Pollux.
To continue our trip across the heavens, turn 90 degrees to your right and face that direction. This summer is not a great time for looking at the other planets in our Solar System. Two of the favourites, Jupiter and Mars will be out between 9-10am and therefore hidden behind the sunlight. That said, although 3.15am is not the most popular show time for planet viewing, the ‘die hard planetarians’ among us may recognise it as a great opportunity to try and see a highly reclusive planet and father to the king of the gods. Uranus, father of Jupiter (king of the planets) may be just about bright enough on this occasion to be seen with the naked eye, but failing that, a pair of binoculars should easily help you spot its ghostly form reflecting light from our star. Even if the planet appears small and dim, bear in mind that it is over 19 Earth-Sun distances (Astronomical Units) away from Earth, and where 1AU represents 150 000 000km, the fact that we can see Uranus at all is a tribute to its considerable size. To locate the gas giant look SSE halfway along the length of the constellation Pisces and a few degrees down.
With the Summer Triangle asterism still taking the prime position in the southern sky to show off its three bright stars, following on from our visit to Vega and Lyra in the top right hand corner last month, let’s now take a closer look at the constellation nearest the horizon.
An ancient star pattern mentioned as far back as 4th Century BC by Eudoxus, this is the constellation of the pet eagle that belonged to the king of the gods, Zeus. Often depicted as flying above a shepherd boy, according to Greek myth, Aquila, the eagle made from gold was ordered to kidnap Ganymede who was then brought to Zeus’ court to be his cupbearer. The pattern contains ten main stars, the brightest of which also forms the bottom point of the Summer Triangle asterism.
For the moment we shall remain looking south, but now drop our eyes down beneath Aquila. Catering for the stargazers among us who like a challenge, our next weapon-bearing star pattern could well test your skills in tracking down a constellation. Viewed from a built up area, this stealthy archer may hide part or all of himself behind trees and rooftops, as even from the clearest skyline observation points little more than the top half of him can ever be spotted above the horizon. Perhaps in our first glance at an artist’s depiction we may think we see a man with a bow and arrow, but closer examination reveals an animal that does not belong to nature. Out of the 88 constellations surrounding our planet in space, Sagittarius, also a sign of the Zodiac, represents one of the colourful mythical creature constellations, for he is a ‘centaur’, half-man, half-horse. Dating back to Babylonian times and bearing the identity of Crotus the inventor of archery, his name was synonymous with a sharp eye and deadly aim. Six bright stars define his bow and arrow which actually point to the centre of the Milky Way galaxy.
So in this case, perseverance brings its own reward as this faintly ‘cloudy’ background, running almost vertically up and to the left of our archer is a positive treasure chest of cosmic wonders for you to feast your eyes upon! That said we need only namedrop a few of them as a bit of independent ‘space-hopping’ with a small telescope or pair of binoculars will reveal plenty besides. One absolute gem that should not be overlooked is Messier 8, or M8 for short, also known by the name the Lagoon Nebula. To find a deep space object 4100 light years away from Earth yet bright enough to be seen with the naked eye is a very rare thing. In fact, it makes up exactly half of an exclusive group of nebulae that can be detected without binoculars or a telescope from mid-northern latitudes. Moreover with an apparent magnitude of 6.0, on a clear night if your eyes are focused on the top of the hunter’s bow, you literally cannot manage to overlook the oval-shaped glow a little farther over on the right hand side. That said, with human night vision abilities being limited, the rods and cones in your eyes will only just be able to register the presence of M8 and so paint it in shades of grey. On the other hand a slow-exposure camera with some zoom capabilities will more honestly capture the Lagoon Nebula in its pinkish colours.
‘Nebula’ is a Latin word for clouds and this interstellar cloud of gas and dust in space represents a huge star-forming region. Originally discovered in 1747, M8 (also designated NGC 6523) has been found to contain a ‘tornado-like’ structure which emits ultraviolet radiation. So to stick with the Sagittarius-‘teapot’ analogy, Messier 8 will be in line with Kaus Borealis (the Northern Bow), the star marking the pointed top of the teapot’s lid, and if we imagine some ornamental stem rising from that lid, the Lagoon nebula will lie even farther over to the right than the star at the top of the stem, yet all the while remaining beneath it.
A little above M8 and requiring a large telescope is the visually smaller but more distant Trifid Nebula, blue on the outside and with a pink interior (when revealed in its true colours), containing some very young hot stars, located about 7600 light years away. Also adjacent to this object is the open star cluster M21, with its harder-to-spot loose conglomeration of stars.
As light is required to either emanate from or reflect off the surface of an object in order for the human eye to be able to detect it, an object that may literally ‘swallow light waves’, effectively making it the blackest of black, would be totally impossible for us to see in the electro-magnetic visible range of light against the blackness of space. Therefore although it be invisible, the fact that we know that a supermassive black hole bearing the name of Sagittarius A* to be precise, perceived by its powerful radio wave emissions, resides at the centre of the Milky Way galaxy, is certainly more than a little exciting to bear in mind while you stargaze in that direction! Furthermore, this proposed black hole would seem to have gained the title ‘supermassive’ for more than just the ring the word has to it, as astrophysicists currently estimate this ravenous cosmic monster to contain over 4 million times the mass of our Sun.
So as you raise your eyes to the heavens to observe the great sights of the night sky in August, happy hunting and enjoy your interstellar voyage!
(Article by Nick Parke, Education Support Officer)